This invention relates to a method and means of determining the relative timing between electrical signals from two or more sources, the signals occurring randomly in time.
Many applications require a measurement of the time at which the first event of a randomly occurring sequence of events occurs and also requires a measurement of the time differences between the first occurring event and each one of a number of later occurring events. An example of such an application is the location of the source of an acoustic wave by determining which of a number of acoustic sensors first detects the wave, which is next to detect the wave, and the time between the successive occurrences. In addition to nondestructive testing of materials, other possible applications include seismic monitoring, sonar direction finding, and the timing of events, as, for example, on a production line. When there is no preferred direction from which signals are expected or no expected order among several signals, it is necessary to have no preferred sensor or time recorder and to allow the first sensor or time recorder that receives a signal to initiate a time sequence. This sensor or time recorder must be disabled from being further actuated during a measuring interval while other sensors or time recorders are left to generate signals terminating the measuring interval when they receive signals. While two sensors are, in general, enough to determine the line along which a wave front moves, the actual direction can be determined and backup information for better precision can be obtained by using more than two sensors. When two sensors alone are used, well-known flip-flop circuits suffice to start and stop the timing measurements. However, no circuits are known to exist that allow any one of a number greater than two sensors to initiate a timing sequence and any other ones of the sensors to provide measures of the time between initiation and receipt of the signal at each of the other sensors.
It is an object of the present invention to provide a measurement of the time difference between two events of a group of two or more events where the order in which the events occur is random.
It is a further object of the present invention to receive signals from three or more sources, to identify which of the sources sent the first signal, and to provide a measure of the time at which a signal was later received from any or all of the other sources.
Other objects will become apparent in the course of a detailed description of the invention.